Swift 2:如何向下转换对象数组

class Animal {
    var name: String
    
    init(name: String) {
        self.name = name
    }
}

class Dog: Animal {
    var breed: String
    
    init(name: String, breed: String) {
        self.breed = breed
        super.init(name: name)
    }
}

class Cat: Animal {
    var color: String
    
    init(name: String, color: String) {
        self.color = color
        super.init(name: name)
    }
}

let animals: [Animal] = [Dog(name: "Buddy", breed: "Golden Retriever"), Cat(name: "Whiskers", color: "Gray")]

var dogs: [Dog] = []
var cats: [Cat] = []

for animal in animals {
    if let dog = animal as? Dog {
        dogs.append(dog)
    } else if let cat = animal as? Cat {
        cats.append(cat)
    }
}

print(dogs) // 输出: [Dog(name: "Buddy", breed: "Golden Retriever")]
print(cats) // 输出: [Cat(name: "Whiskers", color: "Gray")]